The present invention relates to systems for removal of arsenic from water, and more specifically from municipal or rural water systems, utilizing magnesium hydroxide or calcium hydroxide as an adsorbent for arsenic. The present invention also relates to a system for concentrating arsenic in a water sample that allows more accurate, easier, and less expensive laboratory quantification of arsenic in water samples.
Arsenic concentrations in drinking water are a subject of significant concern. It is known that high levels of arsenic in drinking water are carcinogens. The acceptable and safe maximum level of arsenic in drinking water is a subject of significant debate. The current applicable regulations of the United States Environmental Improvement Agency set the maximum limits of arsenic at 50 parts per billion (ppb) in drinking water. However, there are regulatory proposals that the maximum arsenic levels be no more than 10 ppb, and it is advocated by some that maximum arsenic levels be as low as 2 ppb.
Water produced by many municipal water systems, particularly in the western United States as well as other locals, typically has arsenic levels up to about 50 ppb and higher, and thus is commonly higher than proposed lower levels for arsenic, and is in some instances higher than currently accepted levels for arsenic. Some purification means must be employed to remove arsenic prior to consumption of the water. The problem is compounded by the presence of minerals, including carbonates, which interfere with many purification schemes and systems. Particularly with water obtained from areas with geologic evidence of volcanic activity, both high arsenic levels and high mineral content, including carbonates, are typical.
There have been a number of systems used to remove arsenic and other heavy metals from water, including primarily reverse osmosis, column purification, and hydroxide precipitation. Many of these processes provide acceptable results only within narrow and restrictive parameters. In addition, many if not most of these processes are costly and comparatively inefficient.
None of the prior art systems meet the requirements of efficient removal of arsenic utilizing commonly and inexpensively available reagents with a minimum of mechanical processing and steps. Thus there is a need for an inexpensive and simple process that specifically removes arsenic from drinking water, such as municipal water systems and rural well systems.
In addition to the treatment of water to remove arsenic, quantitative measurement of arsenic concentration in water at 1-50 ppb levels requires expensive and complex equipment that is not feasible for small and medium-sized municipal water treatment facilities. There is thus a need for a system for concentrating arsenic from less than 50 ppb to much higher concentrations in water, preferably by a factor of at least 10 to 30 times. The concentration of arsenic to a 100 ppb level and above thereby allows less expensive equipment and less complex techniques to be used for arsenic quantification.
The present invention relates to systems for removing arsenic from water by addition of inexpensive and commonly available magnesium oxide, magnesium hydroxide, calcium oxide, or calcium hydroxide to the water. The hydroxide has a strong chemical affinity for arsenic and rapidly adsorbs arsenic, even in the presence of carbonate in the water. Simple and commercially available mechanical systems for removal of magnesium hydroxide particles with adsorbed arsenic from drinking water can be used, including filtration, dissolved air flotation, vortex separation, or centrifugal separation. A system for continuous removal of arsenic from water is provided. Also provided is a system for concentrating arsenic in a water sample to facilitate quantification of arsenic, by means of magnesium or calcium hydroxide adsorption.